The function of a shunt reactor is generally to provide a required inductive compensation necessary for power line voltage control and stability in high voltage transmission lines or cable systems. The prime requisites of a shunt reactor are to sustain and manage high voltage and to provide a constant inductance over a range of operating inductions. Simultaneously, shunt reactors are to have a low profile in size and weight, low losses, low vibration and noise, and sound structural strength.
A shunt reactor generally comprises a magnetic core composed of one or more core legs, also denoted core limbs, connected by yokes which together form one or more core frames, for each phase. Further, a shunt reactor is made in such a manner that a coil encircles said core leg. It is also well known that shunt reactors are constructed in a manner similar to the core type power transformers in that both use high permeability, low loss grain oriented electrical steel in the yoke sections of the cores. However, they differ markedly in that shunt reactors are designed to provide constant inductance over a range of operating inductions. In conventional high voltage shunt reactors, this is accomplished by use of a number of large air gaps in the core leg, also denoted core limb, section of the reactor core. Said core legs are being fabricated from packets, also denoted core segments, of magnetic material such as electrical steel strips. The core legs are constructed by alternating the core segments with ceramic spacers to provide a required air gap. Said core segments are separated from each other by at least one of said core gaps and said spacers are being bonded onto said core segments with epoxy to form cylindrical core elements. Further, said spacers are typically made of a ceramic material such as steatite. Said core segments are made of high-quality radial laminated steel sheets, layered and bonded to form massive core elements. Further, said core segments are stacked and epoxy bonded to form a core leg with a high modulus of elasticity.
Said core is accommodated in a tank comprising a tank base plate and tank walls together with a foundation supporting the tank. It is also well known that induction devices, such as shunt reactors, are immersed in cooling medium such as oil.
Today, the ceramic spacers are cylinder shaped and typically fill the core gaps to approximately 50-60%. A way to increase the filled area, in said core gaps, is to use hexagonal shaped spacers, and by doing so said spacers can be packed closely together leaving no space between each other.
A problem with this solution is that the cooling of the core segments will be reduced due to major loss of oil flow at the top and bottom core segment surfaces.
Known methods for cooling induction devices, such as transformers or reactors, are Oil Natural Cooling or Oil Force Cooling.
It is a well-known problem that the core gaps are a source of vibrations and noise in an electrical power reactor. Such noise emitted from the reactor must be limited in order not to disturb surrounding areas, and the cost of eliminating said noise becomes prohibitive. Cooling medium, such as oil, will transfer said vibrations from the core gap to the reactor tank, thus causing said noise to be emitted from said induction device. Vibrations are generated since magnetic forces are created when a magnetic flow passes through the core segments and the spacers. Energization of the electrical windings surrounding a magnetic core results in alternating magnetization of the core, and the core segments cyclically expand and contract due to the phenomena of magnetostriction when magnetized and demagnetized by the current flowing in the transformer windings. The phenomenon of magnetostriction means that if a piece of magnetic steel sheet is magnetized, it will extend itself. When said magnetization is interrupted, said sheet will return to its original size. The magnetic core thus acts as a source of 100 Hz or twice the operating frequency of the reactor vibrations and harmonics thereof. The vibrations generated by the magnetic core together with the weight of the core and core assembly may force the rigid base structure beneath a reactor casing into vibration. The casing sidewalls are rigidly connected to the base structure and may be driven into vibration by the stiff base members and propagate noise.
In oil-immersed induction devices to which the present invention relates, the magnetic core is placed in a tank, and the vibrations are propagating by the tank base and the oil to the tank walls are causing noise.